The present invention relates to a method and apparatus for producing slow motion television pictures.
A television picture is generated by displaying discrete video frames each consisting of two interlaced fields. The field rate is usually locked to the frequency of the alternating power supply, thus the US NTSC system displays 60 fields (30 frames) per second and the European PAL system displays 50 fields (25 frames per second). In addition to the video data, synchronising signals are also required to identify each line and field. Thus conventional television receivers require a field synchronising signal 50 or 60 times each second, referred to herein as the broadcast rate.
The problem of showing television pictures in slow motion is that the television receiver must still receive video frame data at the broadcast rate. A known system for satisfying this requirement operates by showing each frame more than once--thus the sequence of video images may be shown at half speed by playing a recording at half speed, writing each frame to a framestore and then reading each frame from the framestore twice at the broadcast rate. However a problem with this known system is that the illusion of movement soon becomes lost and the image is seen as discrete pictures no longer continuous over time.